The present invention is related to a voltage control type control apparatus suitably used in various electronic circuit arrangements requiring correct, or precise controls.
Conventionally, voltage control type control apparatuses arranged by digital circuits and analog circuits are widely known in the field.
One conventional voltage control type control apparatus is arranged as follows: A digital circuit thereof outputs a digital value, and this digital value is D/A-converted so as to produce a control voltage, and then a circuit characteristic of an analog circuit, for instance, a gain of this analog circuit is controlled by using this produced control voltage.
Especially, in order that a total number of interfaces provided on the output side of the digital circuit is reduced and a circuit scale is decreased as to this control signal, either a pulse-duration modulation (PDM) signal or a pulse-width modulation (PWM) signal is used as a digital output in such a voltage control type control apparatus. Also, in general, a simple RC low-pass filter is employed as a D/A converter.
It should be understood that basic operations of the digital outputs are commonly identical to each other either in the case of the pulse-duration modulation signal (will be abbreviated as a "PDM" signal hereinafter) or the pulse-width modulation signal (will be abbreviated a "PWM" signal hereinafter). Since there is no essential difference between them, the following description will be made of the operation by the PDM (pulse-duration modulation) signal.
Roughly speaking, the conventional voltage control type control apparatus with employment of the PDM signal is mainly classified into two different types of control apparatuses, for instance, a first prior art and a second prior art.